This invention relates to positioning apparatus for a centrifugal casting machine and to a method for positioning components of such a machine during a casting operation and during a mold stripping operation. More particularly, the invention relates to bearing apparatus for supporting a drive shaft of a centrifugal casting machine for rotation within a predetermined angular range of tilt about its longitudinal axis, in combination with a plurality of lock pins and associated positioning members for moving a segmented centrifugal casting mold into a predetermined position following the formation of a cast article in the mold, thereby to facilitate retraction of the mold segments from an article cast therein. The invention also comprises a method for accurately positioning a centrifugal casting machine mold during casting rotation thereof and during a mold stripping operation in which segments of a mold are separated to enable a cast article to be removed from the mold.
The use of centrifugal molding apparatus is well known in the foundry art and has long been used to cast smooth surfaced articles such as railroad car wheels, seamless pipes and steel rods. However, the commercial utilization of segmented centrifugal molds to enable the casting of articles having irregular projections on their outer surfaces, such as the projecting cooling fins formed on cast aluminum housings for electric motors, is a relatively recent development, as shown, for example, in U.S. Pat. No. 3,825,057. That patent issued on July 23, 1974 and is assigned to the assignee of the present invention. Consistently reliable operation of such a mold to produce high quality castings can be improved, pursuant to the invention described herein, if the positioning of the mold is carefully controlled during certain casting and mold-stripping cycles.
It has also been discovered that by carefully controlling the positioning of such a mold in the portion of its operating cycle during which mold segments are stripped from an article cast therein, it is possible to realize a substantial savings in material costs. This desirable savings is due to the fact that such controlled positioning of the mold enables the wall thickness of the cast article to be significantly reduced without increasing the risk of the walls being distorted by a mold-stripping operation. Such a reduction in the wall thickness of consistently producible cast motor housings can be achieved, for example, if the position of a segmented mold for casting the housing is aligned accurately with its axis of rotation during an operation in which the casting mold is stripped from the housing. By so aligning the mold, projecting fins on the cast housing are prevented from binding in the mold segments as they are being retracted radially during the mold stripping cycle. On the other hand, if the mold is not accurately aligned with its axis of rotation during such a mold stripping operation, portions of the projecting fins on the housing may become bound in one or more of the mold segments as they are being retracted. Such a momentary binding between these parts frequently causes the cast to be distorted into an elliptical configuration, which often renders the casting unusable for its intended motor housing function. In order to partially counteract such undesirable distortions of motor housings produced by prior art centrifugal casting methods, it was common practice to design relatively thick walled housings so the walls would have greater tensile strength for resisting distortion during a mold-stripping operation. Such thick walls were, in most cases, sufficiently strong to retain their desired cylindrical configurations even when one or more of the retractable mold segments became momentarily bound with the projecting fins of the housing during a mold-stripping operation. Thus, by using such thick walled housing configurations it was possible to avoid an unacceptably high rejection rate of the resultant castings but, of course, the manufacturing expense of the housings was undesirably increased by use of the extra casting metal used to form the thickness of their walls beyond the thickness required solely by their motor housing function.
A further difficulty encountered in the operation of centrifugal casting machines of the type that utilize a segmented mold mounted in cantilever fashion on a bearing-supported drive shaft, is that variable loading of the mold during an operating cycle exerts forces on the operating shaft causing it to either bend or tilt to different angular positions during sequential steps in the casting and mold-stripping cycles of the machine. These variable forces on the drive shaft cause undesirably rapid waer of the drive shaft supporting bearings if those bearings are required to maintain the shaft on a substantially fixed axis during all of the operating cycles of the machine. At the same time, as indicated above, it is desirable to provide positioning means for the shaft that are operable to accurately align it in a predetermined position during a mold-stripping operation in order to avoid binding of the mold segments while they are being retracted from an article cast therein. Thus, it would be desirable to provide a centrifugal casting machine having positioning means for allowing the drive shaft of the machine to be tilted within a predetermined angular range during the various operating cycles of the machine, in combination with positioning means for accurately aligning the mold with its axis of rotation during a mold-stripping operation.